Certain devices such as wafer defect scanners, laser printers, augmented reality devices, document scanners, projectors and the like often employ a laser beam that scans across a surface in a straight or curved line path. These devices employ tilting mirrors to deflect the beam to perform the scanning. These tilting mirrors may be, or may include, Micro Electro Mechanical Systems (“MEMS”) devices. The actuation of mirrors used in MEMS devices, referred to herein as MEMS mirrors, can be via the electromagnetic, electrostatic, piezoelectric, and thermoelectric effects, depending on application.
One type of common MEMS mirror includes a stator and a rotor, with the rotor or structures carried by the rotor being reflective. The stator and/or rotor are driven with a drive signal which results in the rotor oscillating with respect to the stator, thereby changing the angle of reflectance of an incident light beam on the rotor. By oscillating the rotor between two orientations, an opening angle of the mirror is defined, and scanning of the light beam across the surface is accomplished.
Current control schemes for such a MEMS mirror involve the use of a drive signal with a single pulse per each period of mirror oscillation. A single pulse is utilized so as to permit adequate time for sampling of an output signal from the MEMS mirror for use in a control loop.
However, the use of a single pulse brings with it certain drawbacks. For example, in order to achieve a given opening angle, the magnitude of the voltage of the mirror drive signal may be required to be relatively high, and the generation of such high voltages in a portable electronic device may prove burdensome. In addition, the use of a single pulse and the accompanying high voltage may result in spurious drive modes, which is also undesirable.
Therefore, there is a need for new control schemes for MEMS mirrors that overcome these drawbacks.